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Biomedical subjects

T Straub

Publications and source records attributed to T Straub.

15 recordsLinked to original sources
PubMed2005

Health care workers' ability and willingness to report to duty during catastrophic disasters.

Catastrophic disasters create surge capacity needs for health care systems. This is especially true in the urban setting because the high population density and reliance on complex urban infrastructures (e.g., mass transit systems and high rise buildings) could adversely affect the ability to meet surge capacity needs. To better understand responsiveness in this setting, we conducted a survey of health care workers (HCWs) (N =6,428) from 47 health care facilities in New York City and the surrounding metropolitan region to determine their ability and willingness to report to work during various catastrophic events. A range of facility types and sizes were represented in the sample. Results indicate that HCWs were most able to report to work for a mass casualty incident (MCI) (83%), environmental disaster (81%), and chemical event (71%) and least able to report during a smallpox epidemic (69%), radiological event (64%), sudden acute respiratory distress syndrome (SARS) outbreak (64%), or severe snow storm (49%). In terms of willingness, HCWs were most willing to report during a snow storm (80%), MCI (86%), and environmental disaster (84%) and least willing during a SARS outbreak (48%), radiological event (57%), smallpox epidemic (61%), and chemical event (68%). Barriers to ability included transportation problems, child care, eldercare, and pet care obligations. Barriers to willingness included fear and concern for family and self and personal health problems. The findings were consistent for all types of facilities. Importantly, many of the barriers identified are amenable to interventions.

Adolescent↗
PubMed2001

Acf1, the largest subunit of CHRAC, regulates ISWI-induced nucleosome remodelling.

The chromatin accessibility complex (CHRAC) was originally defined biochemically as an ATP-dependent 'nucleosome remodelling' activity. Central to its activity is the ATPase ISWI, which catalyses the transfer of histone octamers between DNA segments in cis. In addition to ISWI, four other potential subunits were observed consistently in active CHRAC fractions. We have now identified the p175 subunit of CHRAC as Acf1, a protein known to associate with ISWI in the ACF complex. Interaction of Acf1 with ISWI enhances the efficiency of nucleosome sliding by an order of magnitude. Remarkably, it also modulates the nucleosome remodelling activity of ISWI qualitatively by altering the directionality of nucleosome movements and the histone 'tail' requirements of the reaction. The Acf1-ISWI heteromer tightly interacts with the two recently identified small histone fold proteins CHRAC-14 and CHRAC-16. Whether topoisomerase II is an integral subunit has been controversial. Refined analyses now suggest that topoisomerase II should not be considered a stable subunit of CHRAC. Accordingly, CHRAC can be molecularly defined as a complex consisting of ISWI, Acf1, CHRAC-14 and CHRAC-16.

Adenosine Triphosphatases↗
PubMed2001

Residues within the N-terminal domain of human topoisomerase I play a direct role in relaxation.

All eukaryotic forms of DNA topoisomerase I contain an extensive and highly charged N-terminal domain. This domain contains several nuclear localization sequences and is essential for in vivo function of the enzyme. However, so far no direct function of the N-terminal domain in the in vitro topoisomerase I reaction has been reported. In this study we have compared the in vitro activities of a truncated form of human topoisomerase I lacking amino acids 1-206 (p67) with the full-length enzyme (p91). Using these enzyme forms, we have identified for the first time a direct role of residues within the N-terminal domain in modulating topoisomerase I catalysis, as revealed by significant differences between p67 and p91 in DNA binding, cleavage, strand rotation, and ligation. A comparison with previously published studies showing no effect of deleting the first 174 or 190 amino acids of topoisomerase I (Stewart, L., Ireton, G. C., and Champoux, J. J. (1999) J. Biol. Chem. 274, 32950-32960; Bronstein, I. B., Wynne-Jones, A., Sukhanova, A., Fleury, F., Ianoul, A., Holden, J. A., Alix, A. J., Dodson, G. G., Jardillier, J. C., Nabiev, I., and Wilkinson, A. J. (1999) Anticancer Res. 19, 317-327) suggests a pivotal role of amino acids 191-206 in catalysis. Taken together the presented data indicate that at least part(s) of the N-terminal domain regulate(s) enzyme/DNA dynamics during relaxation most probably by controlling non-covalent DNA binding downstream of the cleavage site either directly or by coordinating DNA contacts by other parts of the enzyme.

Catalysis↗
PubMed2000

Active DNA topoisomerase IIalpha is a component of the salt-stable centrosome core.

Recently, we reported that the monoclonal antibody specific for human DNA topoisomerase IIalpha, Ki-S1, stains not only the nuclei of human A431 cells but also extranuclear structures suggestive of centrosomes (Meyer, K. N., Kjeldsen, E., Straub, T., Knudsen, B. K., Kikuchi, A., Hickson, I. D., Kreipe, H., and Boege, F. (1997) J. Cell Biol. 136, 775-788). Here, we confirm colocalization of Ki-S1 with the centrosomal marker gamma-tubulin. In addition, we show labeling of centrosomes by peptide antibodies against the N and C termini of human topoisomerase IIalpha. Probing Western blots of isolated centrosomes with topoisomerase IIalpha antibodies, we demonstrate a protein band of 170 kDa. Moreover, isolated centrosomes exhibited DNA decatenation and relaxation activity correlated to the amount of topoisomerase IIalpha protein in the same way as seen in the pure recombinant enzyme. Topoisomerase IIalpha epitopes could not be removed from centrosomes by salt extraction, DNase treatment, or RNase treatment, procedures that completely removed the enzyme from nuclei. Taken together, these observations suggest that active topoisomerase IIalpha is bound tightly to the centrosome in a DNA-independent manner. Because such centrosomal topoisomerase IIalpha was also present in quiescent lymphocytes devoid of topoisomerase IIalpha in the nuclei, we assume that it might be a long-lived storage form.

Animals↗
PubMed2000

PSF/p54(nrb) stimulates "jumping" of DNA topoisomerase I between separate DNA helices.

We have previously shown [Straub et al. (1998) J. Biol. Chem. 273, 26261] that the pyrimidine tract binding protein associated splicing factor PSF/p54(nrb) binds and stimulates DNA topoisomerase I. Here we show that cleavage and religation half-reactions of topoisomerase I are unaffected by PSF/p54(nrb), whereas the propensity of the enzyme to jump between separate DNA helices is stimulated. To demonstrate such an effect, topoisomerase I was first captured in suicidal cleavage of an oligonucleotide substrate. Subsequently, a cleavage/ligation equilibrium was established by adding a ligation donor under conditions allowing recleavage of the ligated substrate. Finally, a second oligonucleotide was added to the mixture, which also allowed suicidal cleavage by topoisomerase I, but did not accommodate the ligation donor of the first oligonucleotide. Thus, topoisomerase I was given the choice to engage in repeated cleavage/ligation cycles of the first oligonucleotide or to jump to the second suicide substrate and get trapped. PSF/p54(nrb) enhanced the cleavage rate of the second oligonucleotide (11-fold), suggesting that it stimulates the dissociation of topoisomerase I after ligation. Thus, stimulation of topoisomerase I catalysis by PSF/p54(nrb) seems to be affected by mobilization of the enzyme.

Base Sequence↗
PubMed1999

New haemostatic techniques: argon plasma coagulation.

Bleeding is one of the main challenges for endoscopists. Despite a large number of methods for haemostasis, several types of haemorrhage lack an adequate therapeutic remedy. Argon plasma-coagulation (APC), a new method for the non-contact application of high-frequency current, promises to solve many of these problems. Among 1164 patients treated in 2349 sessions using APC, the indication was bleeding (due to tumour, intervention, angiodysplasia or coagulation disorders) in 305 patients (26%). The primary success rate was over 99%, the rebleeding rate 1.6% and the complication rate less than 1%, with zero mortality. Physical principles, indications, application parameters and results are discussed, especially in comparison with the Nd:YAG laser. APC is a new, efficacious, safe and easy-to-use method for the devitalization of tissue and haemostasis, especially in problematic cases.

Adolescent↗
PubMed1998

Essential mitotic functions of DNA topoisomerase IIalpha are not adopted by topoisomerase IIbeta in human H69 cells.

Unique functions of mammalian DNA-topoisomerases IIalpha and -beta are suggested by their distinct cellular distribution and chromatin binding at mitosis. Here, we studied H69-VP cells that, due to a homozygous mutation, express topoisomerase IIalpha mostly outside the nucleus. In these cells topoisomerase IIbeta showed a normal nuclear localization. However, at mitosis it diffused away from the chromatin despite the nuclear lack of the alpha-isoform. 80% of these cells performed chromosome condensation and disjunction with the aid of cytosolic topoisomerase IIalpha, which bound to the mitotic chromatin with low affinity. However, the genotype of these cells was highly polyploid indicating an increased rate of non-disjunction. In 20% of the mutant cells neither topoisomerase II isoform was bound to the mitotic chromatin, which appeared as an unstructured DNA spheroid unable to undergo disjunction and cytokinesis. Parental H69 cells expressing topoisomerase IIalpha inside the nucleus exhibited high affinity binding of the enzyme to the mitotic chromatin. Their genotype was mostly diploid and stable. We conclude (i) that high affinity chromatin binding of topoisomerase IIalpha is essential for chromosome condensation/disjunction and (ii) that topoisomerase IIbeta does not adopt these functions.

Antigens, Neoplasm↗
PubMed1998

The RNA-splicing factor PSF/p54 controls DNA-topoisomerase I activity by a direct interaction.

DNA-topoisomerase I has been implied in RNA splicing because it catalyzes RNA strand transfer and activates serine/arginine-rich RNA-splicing factors by phosphorylation. Here, we demonstrate a direct interaction between topoisomerase I and pyrimidine tract binding protein-associated splicing factor (PSF), a cofactor of RNA splicing, which forms heterodimers with its smaller homolog, the nuclear RNA-binding protein of 54 kDa (p54). Topoisomerase I, PSF, and p54 copurified in a 1:1:1 ratio from human A431 cell nuclear extracts. Specific binding of topoisomerase I to PSF (but not p54) was demonstrated by coimmunoprecipitation and by far Western blotting, in which renatured blots were probed with biotinylated topoisomerase I. Chemical cross-linking of pure topoisomerase I revealed monomeric, dimeric, and trimeric enzyme forms, whereas in the presence of PSF/p54 the enzyme was cross-linked into complexes larger than homotrimers. When topoisomerase I was complexed with PSF/p54 it was 16-fold more active than the pure enzyme, which could be stimulated 5- and 16-fold by the addition of recombinant PSF or native PSF/p54, respectively. A physiological role of this stimulatory mechanism seems feasible, because topoisomerase I and PSF showed a patched colocalization in A431 cell nuclei, which varied with cell cycle.

Catalysis↗
PubMed1997

The dihydropyridine dexniguldipine hydrochloride inhibits cleavage and religation reactions of eukaryotic DNA topoisomerase I.

Dexniguldipine hydrochloride (B859-35, a dihydropyridine with antitumor and multidrug resistance-reverting activity) inhibits both the DNA cleavage and religation reactions of purified human DNA topoisomerase I at concentrations >1 microM, whereas at concentrations <1 microM it inhibits selectively the religation step and stabilizes the covalent topoisomerase I-DNA intermediate in a similar fashion as camptothecin. Inhibition of religation by camptothecin can be overcome by increasing the concentration of the DNA substrate in the religation reaction, indicating a competitive type of inhibition. In contrast, dexniguldipine hydrochloride decreases rate constants of topoisomerase I-mediated DNA religation independently of the concentration of the DNA substrate, suggesting a noncompetitive mechanism of inhibition, which is different from that of camptothecin.

Antineoplastic Agents↗
PubMed1997

Cell cycle-coupled relocation of types I and II topoisomerases and modulation of catalytic enzyme activities.

We visualized DNA topoisomerases in A431 cells and isolated chromosomes by isoenzyme-selective immunofluorescence microscopy. In interphase, topoisomerase I mainly had a homogeneous nuclear distribution. 10-15% of the cells exhibited granular patterns, 30% showed bright intranucleolar patches. Topoisomerase II isoenzymes showed spotted (alpha) or reticular (beta) nuclear patterns throughout interphase. In contrast to topoisomerase IIalpha, topoisomerase IIbeta was completely excluded from nucleoli. In mitosis, topoisomerase IIbeta diffused completely into the cytosol, whereas topoisomerases I and IIalpha remained chromosome bound. Chromosomal staining of topoisomerase I was homogeneous, whereas topoisomerase IIalpha accumulated in the long axes of the chromosome arms and in the centriols. Topoisomerase antigens were 2-3-fold higher in mitosis than in interphase, but specific activities of topoisomerase I and II were reduced 5- and 2.4-fold, respectively. These changes were associated with mitotic enzyme hyperphosphorylation. In interphase, topoisomerases could be completely linked to DNA by etoposide or camptothecin, whereas in mitosis, 50% of topoisomerase IIalpha escaped poisoning. Refractoriness to etoposide could be assigned to the salt-stable scaffold fraction of topoisomerase IIalpha, which increased from <2% in G1 phase to 48% in mitosis. Topoisomerases I and IIbeta remained completely extractable throughout the cell cycle. In summary, expression of topoisomerases increases towards mitosis, but specific activities decrease. Topoisomerase IIbeta is released from the heterochromatin, whereas topoisomerase I and IIalpha remain chromosome bound. Scaffold-associated topoisomerase IIalpha appears not to be involved in catalytic DNA turnover, though it may play a role in the replicational cycle of centriols, where it accumulates during M phase.

Antibody Specificity↗
PubMed1996

Separation and functional analysis of eukaryotic DNA topoisomerases by chromatography and electrophoresis.

DNA topoisomerases are enzymes that control DNA topology by cleaving and rejoining DNA strands and passing other DNA strands through the transient gaps. Consequently, these enzymes play a crucial role in the regulation of the physiological function of the genome. Beyond their normal functions, topoisomerases are important cellular targets in the treatment of human cancers. In this review we summarize current protocols for extracting and purifying DNA topoisomerases, and for separating subtypes and isoforms of these enzymes. Furthermore, we discuss methods for measuring the catalytic activity of topoisomerases and for monitoring the molecular effects of topoisomerase-directed antitumor drugs in cell-free assays.

Base Sequence↗
PubMed1996

Selected novel flavones inhibit the DNA binding or the DNA religation step of eukaryotic topoisomerase I.

Topoisomerases are involved in many aspects of DNA metabolism such as replication and transcription reactions. Camptothecins, which stabilize the covalent intermediate of topoisomerase I and DNA are effective, though toxic, drugs for cancer therapy. In this study, a new class of topoisomerase I inhibitors was identified, and their mode of action was characterized using recombinant human topoisomerase I preparations and human HL-60 leukemic cells. Quercetin and the related natural flavones, acacetin, apigenin, kaempferol, and morin, inhibit topoisomerase I-catalyzed DNA religation. In contrast to camptothecin, these compounds do not act directly on the catalytic intermediate and also do not interfere with DNA cleavage. However, formation of a ternary complex with topoisomerase I and DNA during the cleavage reaction inhibits the following DNA religation step. 3,3',4',7-Tetrahydroxy-substituted flavones stabilize the covalent topoisomerase I-DNA intermediate most efficiently. Enhanced formation of covalent topoisomerase I-DNA complexes was also demonstrated in human HL-60 cells. In contrast, synthetic 3,5'-dibromo- 4'-hydroxy-3-methylflavones bind selectively to topoisomerase I in its non-DNA-bound form and block the following DNA binding step. As a consequence, these synthetic flavonoids are capable of counteracting topoisomerase I-directed effects of camptothecin. Inhibition of DNA binding is obtained by voluminous hydrophobic substituents in 6-position of the flavone structure. Our data show that selective inhibitors of both half-reactions of topoisomerase I can be derived from the flavone structure.

Base Sequence↗
PubMed1988

Acute anterior cruciate ligament repair.

Sixty-six consecutive patients with acute repair of a complete isolated anterior cruciate ligament (ACL) injury were retrospectively reviewed to evaluate the effectiveness of the authors' surgical technique. All patients noted either a pop, acute swelling, or had acute disability after injury with 58% experiencing all three signs and symptoms. Preoperative testing without anesthesia revealed 95% of patients to have either a positive modified Losee or Lachman test. Postoperative results were obtained by questionnaire in 41 of 42 patients (98%) with a minimum two-year follow-up period. Physical examination was completed in 32 (76%) and arthrometer testing in 30 (71%) patients. Subjective results were good or better in 91%. No patients had buckling or meniscal loss postoperatively. Patellofemoral pain, however, was significant in 15% and severe in 2%. Postoperative functional results were good or better in 78% with all patients participating in sports, 76% in "at risk" sports. A Performance Quotient (P.Q.) was developed to more accurately correlate preinjury and postoperative function. The average P.Q. was 0.87. Objective results were good or better in 100%. Stability was within normal limits by clinical observation in 88%, and by arthrometer testing in 87%. ACL repair is recommended in the young patient who is active in "at risk" sports and who is unwilling to modify activities and willing to undergo a one-year rehabilitation period.

Acute Disease↗